Casing for a writing instrument



FIG. 1 is a front elevational view of a casing for a writing instrument showing my new design;

FIG. 2 is a left side elevational view, the right side being a mirror image thereof;

FIG. 3 is a rear elevational view;

FIG. 4 is a bottom plan view;

FIG. 5 is a top plan view;

FIG. 6 is a front elevational view with the cap member removed for convenience of illustration; and,

FIG. 7 is a left side elevational view of FIG. 6, the right side being a mirror image thereof.

The pen nib depicted by means of broken lines in FIGS. 6 and 7 is shown for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a casing for a writing instrument, as shown and described. 